Hurricane IRWIN

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HURRICANE IRWIN DISCUSSION NUMBER 7
NWS NATIONAL HURRICANE CENTER MIAMI FL EP112011
200 PM PDT FRI OCT 07 2011
THE CLOUD PATTERN OF THE HURRICANE HAS BECOME A LITTLE BETTER
ORGANIZED OVER THE PAST SEVERAL HOURS WITH MORE DEFINITIVE BANDING
FEATURES AND THE EYE BECOMING APPARENT ON VISIBLE IMAGES. TAKING A
BLEND OF DVORAK INTENSITY ESTIMATES FROM TAFB AND SAB YIELDS AN
INITIAL INTENSITY ESTIMATE OF 80 KT. IRWIN IS CURRENTLY IN AN
ENVIRONMENT OF MODEST EASTERLY SHEAR...BUT IN A COUPLE OF DAYS THIS
SHEAR IS FORECAST TO INCREASE. THEREFORE...THE STRENGTHENING TREND
IS PREDICTED TO END IN 36 TO 48 HOURS...AND THE OFFICIAL INTENSITY
FORECAST IS VERY SIMILAR TO THE LATEST STATISTICAL-DYNAMICAL
GUIDANCE. SOME OF THE DYNAMICAL GUIDANCE INDICATES RESTRENGTHENING
NEAR THE END OF THE FORECAST PERIOD...BUT GIVEN THE UNCERTAINTIES
IN PREDICTING INTENSITY CHANGE AT 5 DAYS...THE OFFICIAL FORECAST
DOES NOT GO WITH THAT SCENARIO.
THE MOTION CONTINUES TO SLOW AND IS NOW ABOUT 295/5. AS THE
MID-LEVEL RIDGE TO THE NORTHEAST OF IRWIN RETREATS TO THE EAST AND
SOUTH...THE TROPICAL CYCLONE IS FORECAST TO TURN TOWARD THE RIGHT
OVER THE NEXT COUPLE OF DAYS. THEREAFTER IRWIN SHOULD BEGIN MOVING
EASTWARD WITHIN A REGION OF BROAD WESTERLY LOW- TO MID-LEVEL FLOW.
SOME OF THE TRACK GUIDANCE SUCH AS THE GFS IS NOT TAKING IRWIN AS
FAR EAST AS PREVIOUSLY. THIS IS CONSISTENT WITH THAT MODEL SHOWING
A MID-TROPOSPHERIC RIDGE BEGINNING TO BUILD TO THE NORTH OF IRWIN
BY DAY 5. THE OFFICIAL TRACK FORECAST GENERALLY LIES BETWEEN THE
GFS AND THE LATEST ECMWF TRACK.
FORECAST POSITIONS AND MAX WINDS
INIT 07/2100Z 14.0N 120.9W 80 KT 90 MPH
12H 08/0600Z 14.2N 121.2W 85 KT 100 MPH
24H 08/1800Z 14.7N 121.2W 90 KT 105 MPH
36H 09/0600Z 14.8N 120.6W 90 KT 105 MPH
48H 09/1800Z 15.0N 119.5W 85 KT 100 MPH
72H 10/1800Z 15.0N 117.0W 75 KT 85 MPH
96H 11/1800Z 15.5N 113.0W 70 KT 80 MPH
120H 12/1800Z 16.5N 109.0W 65 KT 75 MPH
$$
FORECASTER PASCH
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